U.S. Pat. No. 4,470,309 describes various embodiments of electromagnetic flow sensors comprising
a metallic measuring tube through which flows an electrically conductive fluid to be measured and whose inner surface is lined with an insulating layer, PA0 which has at least two measuring electrodes, and PA0 at which means are provided for generating a magnetic field passing through the measuring tube which comprise: PA0 a magnetically shielded casing enclosing the coils and the coil cores with the pole pieces, which also serves to close the magnetic circuit, thus acting as a magnetic return path. PA0 a metallic measuring tube through which flows an electrically conductive fluid to be measured and whose inner surface is lined with an insulating layer, PA0 a plastic measuring tube through which flows an electrically conductive fluid to be measured, PA0 a magnetically shielded casing which surrounds the saddle-shaped coils and coil cores and also serves to close the magnetic circuit, thus acting as a magnetic return path. PA0 a measuring tube of insulating material through which flows an electrically conductive fluid to be measured, PA0 a nonferromagnetic metallic measuring tube through which flows an electrically conductive fluid to be measured and whose inside surface is lined with an insulating layer, PA0 an enclosure surrounding the coils and/or the coil cores and/or the pole stampings or regions and/or the return-path stampings or regions. PA0 a ceramic measuring tube or plastic measuring tube through which flows an electrically conductive fluid to be measured, PA0 an enclosure surrounding the coils and/or the coil cores and/or the pole stampings or regions and/or the return-path stampings or regions. PA0 a nonferromagnetic metallic measuring tube through which flows an electrically conductive fluid to be measured and whose inside surface is lined with an insulating layer, PA0 an enclosure surrounding the coils and/or the coil cores and/or the pole stampings or regions and/or the return-path stampings or regions. PA0 a ceramic measuring tube or plastic measuring tube through which flows an electrically conductive fluid to be measured, PA0 an enclosure surrounding the coils and/or the coil cores and/or the pole stampings or regions and/or the return-path stampings or regions. PA0 two coils whose respective axes are perpendicular to the axis of the measuring tube, and PA0 two U-shaped coil cores per coil
coils disposed diametrically opposite to each other outside the outer surface of the measuring tube, PA1 coil cores, and PA1 pole pieces formed thereon which extend to or rest on the outer surface of the measuring tube, as well as PA1 which has at least two measuring electrodes, and PA1 at which means are provided for generating a magnetic field passing through the measuring tube which comprise: PA1 which has at least two measuring electrodes, PA1 at which means are provided for generating a magnetic field passing through the measuring tube which comprise saddle-shaped coils with coil cores disposed diametrically opposite to each other on the outside surface of the measuring tube, and PA1 which has at least two measuring electrodes, PA1 at which means are provided for generating a magnetic field passing through the measuring tube which comprise saddle-shaped coils with coil cores disposed diametrically to each other on the outside surface of the measuring tube and stacked laminations which are formed on the coils on both sides thereof, form respective air gaps in the areas of the measuring electrodes, end in pole pieces, and act as magnetic return paths, PA1 whose nominal diameter is 200 mm to 700 mm, PA1 which has at least two measuring electrodes, and PA1 at which means are provided for generating a magnetic field passing through the metallic measuring tube which comprise: PA1 whose nominal diameter is 200 mm to 700 mm, PA1 which has at least two measuring electrodes, and PA1 at which means are provided for generating a magnetic field passing through the ceramic measuring tube or plastic measuring tube which comprise: PA1 whose nominal diameter is greater than 500 mm, PA1 which has at least two measuring electrodes, and PA1 at which means are provided for generating a magnetic field passing through the metallic measuring tube which comprise: PA1 whose nominal diameter is greater than 500 mm, PA1 which has at least two measuring electrodes, and PA1 at which means are provided for generating a magnetic field passing through the ceramic measuring tube or plastic measuring tube which comprise: PA1 The enclosure no longer serves as a magnetic return path but only has a mechanical protective function and, in the case of a metal casing, a magnetic shielding function; PA1 pole pieces and magnetic return path are implemented with sheet stampings or stacked laminations resting on the outside surface of the measuring tube or with pole regions forming part of the measuring tube, so that the material consumption for pole pieces and magnetic return path depends only on the respective diameter of the measuring tube and is thus minimized; PA1 the coils require only justifiably little copper, but very much less than the saddle-shaped coils of the prior art; PA1 the magnetic system is very easy to assemble, and PA1 the extent of the magnetic field in the direction of the axis of the measuring tube is shorter than in the conventional arrangements, so that the measuring tube can also be made shorter than usual, whereby a further cost reduction is achieved since, in addition to copper, measuring-tube material can be saved. With saddle-shaped coils, the measuring-tube length must be at least 1.5 times the nominal diameter, while in the invention, only 1.3 times the nominal diameter is necessary. PA1 whose leg length is little greater than the length of the coils, PA1 one leg of each of which extends into the respective coil and is magnetically coupled to the pole stampings or regions, with the legs in the respective coils separated by a given distance, and PA1 whose respective legs which are not in the respective coils are magnetically coupled to the return-path stampings or regions.
DE-B 20 40 682 describes an electromagnetic flow sensor comprising
saddle-shaped coils disposed diametrically opposite to each other outside the outer surface of the measuring tube, and PA2 stacked laminations completely surrounding the central portions of the saddle-shaped coils for closing the magnetic circuit, thus acting as a magnetic return path. PA2 a compensating magnetic field being generated between said pole pieces in the area of the measuring electrodes which is directed oppositely to the magnetic field. PA2 non-saddle-shaped coils disposed diametrically opposite to each other at the outside surface of the metallic measuring tube, PA2 coil cores, PA2 pole pieces of soft magnetic material which extend on both sides of the respective non-saddle-shaped coil in the circumferential direction either as pole stampings on the inside or outside surface of the metallic measuring tube or as pole regions put in the metallic measuring tube, with their ends separated by a sufficient distance, PA2 either two soft magnetic return-path stampings each disposed on one side of the coils and of the pole stampings or regions and resting on the outside or inside surface of the metallic measuring tube and completely surrounding the latter, PA2 or two soft magnetic return-path regions each put in and completely surrounding the metallic measuring tube on one side of the coils and of the pole stampings or regions, PA2 non-saddle-shaped coils disposed diametrically opposite to each other at the outside surface of the ceramic measuring tube or plastic measuring tube, PA2 coil cores, PA2 pole pieces of soft magnetic material which extend on both sides of the respective coil in the circumferential direction and PA2 either two soft magnetic return-path stampings each embedded in the plastic measuring tube or resting on the outside surface of the ceramic measuring tube or plastic measuring tube on one side of the coils and of the pole stampings or regions PA2 or two return-path regions each provided on one side of the coils and of the pole stampings or regions and forming a soft magnetic conductive section of the ceramic measuring tube or plastic measuring tube, PA2 non-saddle-shaped pairs of coil sections disposed diametrically opposite to each other at the outside surface of the metallic measuring tube, PA2 one U-shaped coil core per coil section PA2 pole pieces of soft magnetic material which extend on both sides of the respective pair of coil sections in the circumferential direction either as pole stampings on the outside or inside surface of the metallic measuring tube or as pole regions put in the metallic measuring tube, with their ends separated by a sufficient distance, PA2 either two soft magnetic return-path stampings each disposed on one side of the coils and the pole stamping or regions and resting on the outside or inside surface of the metallic measuring tube and completely surrounding the latter PA2 or two soft magnetic return-path regions each put in the metallic measuring tube on one side of the pairs of coil sections and of the pole stampings or regions and completely surrounding the metallic measuring tube, PA2 non-saddle-shaped pairs of coil sections disposed diametrically opposite to each other at the outside surface of the ceramic measuring tube or plastic measuring tube PA2 one U-shaped coil core per coil section PA2 pole pieces of soft magnetic material on both sides of the respective pair of coil sections in the circumferential direction which PA2 either two soft magnetic return-path stampings each embedded in the plastic measuring tube or resting on the outside surface of the ceramic measuring tube or plastic measuring tube on one side of the pair of coil sections and of the pole stampings or regions, PA2 or two return-path regions each provided on one side of the pair of coil sections and of the pole stampings or regions and forming a soft-magnetically conductive section of the ceramic measuring tube or plastic measuring tube,
U.S. Pat. No. 4,774,844 describes an electromagnetic flow sensor comprising
WO-A 91/11731 discloses an electromagnetic flow sensor comprising
The manufacturing costs of such electromagnetic flow sensors increase disproportionately toward great nominal diameters, particularly above 200 mm up to 2000 mm, especially since, to achieve a sufficient magnetic field strength, the coils and the coil cores/pole pieces or the saddle-shaped coils/coil cores must be made correspondingly large, which requires large quantities of copper for the coils, particularly for the saddle-shaped coils, and correspondingly large quantities of material for the coil cores/pole pieces.